1. Field of the Invention
The present invention relates to a curable silicone resin composition that is useful as a sealing material for optical semiconductors, as well as a sealing material for optical semiconductors comprising such a composition, and an optical semiconductor device that has been sealed with a cured product of such a composition.
2. Description of the Prior Art
Examples of known conventional optical semiconductors include light receiving elements such as the various photodiodes and phototransistors used as optical sensors, and light emitting diodes (LED), and epoxy resins are typically used as the sealing material for these optical semiconductors. Tests have also been conducted on the use of silicone resins as sealing materials (see patent reference 1 and patent reference 2), although examples of practical application of such resins are rare.
In recent years, white LEDs have been attracting considerable attention, and there is a trend towards the use of LEDs that emit light at shorter wavelengths. Meanwhile there is also a trend towards increased use of light receiving elements that use high energy laser light as a detection target. In this environment, resolving the problems associated with epoxy resin sealing materials, such as a deterioration in the transparency, or coloring such as yellowing, caused by continuous or long-term transmittance of ultraviolet light or the like, has become critical. As a result, silicone resins that produce cured products with excellent ultraviolet light transmittance are being investigated as potential alternative sealing materials to conventional epoxy resins. However, with conventional silicone resins, it has proven very difficult to satisfactorily prevent the deterioration of the optical characteristics over time, meaning practical application of these materials has been impossible.
On the other hand, it is generally well known that adding a combination of a phenol-based antioxidant and a photostabilizer to a thermoplastic resin improves the heat resistance, the photostability and the weather resistance of the resin. Furthermore, investigations are also being conducted into improving the weather resistance by adding a combination of a phenol-based antioxidant and a hindered amine compound to a plastic such as polypropylene (see non-patent reference 1).
[Patent Reference 1] JP10-228249A.
[Patent Reference 2] U.S. Pat. No. 5,998,925.
[Non-Patent Reference 1] Up-to-date Technology of Polymer Additives (CMC Publishing Co., Ltd., 1988).